1. Field of the Invention
The invention relates to variable rate ink jet printing. More specifically, the invention concerns the use of a compare match timer and direct memory access to transmit column data from memory to an ink jet firing circuit at a rate that creates a correct column pitch for any document speed.
2. Background Art
Banks, credit unions and other financial institutions often image checks, deposit slips and other types of bank documents in order to process financial transactions efficiently. Document processing systems have therefore become quite prevalent in the industry. A typical document processing system also uses an ink jet endorser for checks and other banking documents. To produce dot matrix style text on a paper document traveling through a document processor, a fixed ink jet head is used. As the paper travels past the head""s position, dots are fired in the proper sequence to form characters. Thus, it is desirable to allow improved allocation of resources by efficient division of processing tasks.
Another concern is the fact that document processing systems often require the endorser to operate at a variable document travel rate. This mode of operation means that the rate at which documents travel through the system varies based on the particular circumstances. Variable rate printing has typically required a microprocessor to determine the correct column pitch for a given document travel rate. Both the determination of the correct pitch and the actual transfer of the column data occupies valuable processing time, reduces overall efficiency, and increases costs. Current systems fail to appreciate that a substantial portion of these activities can be effectively delegated. This failure to delegate routine timing functions to more appropriate resources translates into additional processing time and reduced system performance. It is therefore desirable to allow variable rate printing while freeing the host processor for other tasks and thereby eliminating the real-time burden of controlling the column and dot timing.
In a first aspect of the invention, an endorser control system comprises a processor having a DMA unit for retrieving column data at a column data rate wherein the processor controls the variable document travel rate. The system further comprises a sequencer for converting the column data into dot data. The DMA unit thus writes the column data from the processor memory to the sequencer at the specified column data rate. The control system further comprises a compare match timer for matching the column data rate to the variable document travel rate.
In a second aspect of the invention, a document endorser comprises a DMA-based control system for generating dot data and controlling a variable document travel rate, and a firing circuit having a nozzle array with at least one column of nozzles. The circuit provides the nozzle array with a signal converted from the dot data.
In a third aspect of the invention, a method for controlling a variable rate ink jet printer comprises the step of storing column data in a processor memory wherein the column data corresponds to the information to be printed. The method further comprises the steps of matching the column data rate to a variable document travel rate and directly accessing the column data and the processor memory at the column data rate. The method also includes the step of converting the column data into dot data.